This application relates to identification of abnormal traces during electrochemical determination of analytes such as glucose, and to a meter, and meter-test strip combination for use in such a method.
Small disposable electrochemical test strips are frequently used in the monitoring of blood glucose by diabetics. Such test strips can also be employed in the detection of other physiological chemicals of interest and substances of abuse. In general, the test strip comprises at least two electrodes and appropriate reagents for the test to be performed, and is manufactured as a single use, disposable element. The test strip is combined with a sample such as blood, saliva or urine before or after insertion in a reusable meter, which contains the mechanisms for detecting and processing an electrochemical signal from the test strip into an indication of the presence/absence or quantity of the analyte determined by the test strip.
Electrochemical detection of glucose is conventionally achieved by applying a potential to an electrochemical cell containing a sample to be evaluated for the presence/amount of glucose, an enzyme that oxidizes glucose, such as glucose oxidase, and a redox mediator. As shown in FIG. 1, the enzyme oxidizes glucose to form gluconolactone and a reduced form of the enzyme. Oxidized mediator reacts with the reduced enzyme to regenerate the active oxidase and produced a reduced mediator. Reduced mediator is oxidized at one of the electrodes, and then diffuses back to either be reduced at the other electrode or by the reduced enzyme to complete the cycle, and to result in a measurable current. The measured current is related to the amount of glucose in the sample, and various techniques are known for determining glucose concentrations in such a system are known. (See for example, U.S. Pat. Nos. 6,284,125; 5,942,102; 5,352,351; and 5,243,516, which are incorporated herein by reference.)
In meters that analyze electrochemical signals, assumptions are made about the characteristics of the signal in order to minimize the processing capability that is required in the meter, and processing time that is required. Not all traces, however, will meet these ideal characteristics. For example, when a user contacts the test strip twice in a short period of time, uses an inappropriate sample, flicks the end of the test strip, the signal characteristics may be abnormal. Other sources of signal abnormality may include use of a wet or damp test strip, or a test strip in which parts of the reagent have come loose from the surface of the working electrode. Abnormal signals of this type can still produce a result, but because the data processing assumes signal characteristics that are not in fact present, the result is unreliable. It would therefore be desirable to have a method for identifying abnormal traces that did not require significant processing or add additional component requirements to the meter or test strips.